In recent years, there have been active study on achieving much more lightweight of a structure by using a fiber reinforced composite material in a structural material of a housing of an electronic device or an automobile. In production of the fiber reinforced composite material, a fiber having a sufficient length for a roller to convey in a process and having a form of a combination of multiple single filaments each having a thickness (diameter) of several μm, that is, form reinforcing fibers in strands form (reinforcing fiber strands), is appropriately processed and used as a reinforcing fiber in many cases.
In the related art, as a method of using the reinforcing fiber strands in the fiber reinforced composite material, a method, in which thick reinforcing fiber strands containing a large number of constituent single filaments is produced, the strands are widened or the like such that thin flat reinforcing fiber strands are made, and the thin flat strands are used directly or the thin flat strands are subjected to separating and then are used, have been known as a preferable method in terms of cost reduction.
As a method for widening the reinforcing fiber strands, a method for dispersing constituent fibers in a width direction by applying a water current or a high-pressure air current to the reinforcing fiber strands, a method for spreading strands by applying, to the strands in the air or in a liquid, vibration generated due to an ultrasonic wave or the like (PTL 1 or PTL 2), a method for extending and spreading strands through contact between the strands and a widening jig (for example, PTL 3), or the like has been known.
In addition, as a separating technology, a method for continuously separating reinforcing fiber strands by using a comb-like jig (PTL 4), a method for separating strands by actively cutting a single filament having a variation in a positional relationship in the reinforcing fiber strands in a length direction (PTL 5), or the like has been known. However, since it is possible to achieve more cost down due to the fiber reinforced composite material, there is a demand for a method for stable and mass production of yarns separated from the reinforcing fiber strands.